# Protease --- A **protease** is a [[digestive enzymes|digestive enzyme]] that breaks down the [[covalent bond|peptide bonds]] in [[protein|proteins]]. They're very specific on the type of peptide bond they break. For example, [[pancreas|trypsin]] only cleaves the bonds between arginine and lysine (both positively charged), and **chymotrypsin** only cleaves bonds between hydrophobic amino acids. **Carboxypeptidase** cleaves any bonds, but only those connecting the last amino acid (on the carboxyl end) on the chain (i.e. it pops one off the end at a time). **Pepsin** is a protease made by [[gastric gland|chief cells]] in the stomach. Chief cells secrete a enzyme precursor called **pepsinogen**, which reacts with [[stomach acid|HCl]] in the stomach to form pepsin. If the [[gastric gland|chief cell]] were to make it in the activated form, it would end up digesting itself! Not good! In addition to nutrient digestion, proteases can be used offensively as well. [[T-cells]] release proteases to destroy pathogenic [[bacteria]]. ___